A new cancer immunosuppression target: Indoleamine 2,3-dioxygenase (IDO). A review of the IDO mechanism, inhibition and therapeutic applications

Indoleamine 2,3-dioxygenase (IDO) has recently been implicated in tumor immune escape. In particular, IDO undermines a vigorous antitumor immune response by promoting peripheral tolerance, thereby shaping the host environment to be more hospitable to tumor survival and growth. Consequently, the development of potent IDO inhibitors that compromise this toleragenic mechanism is an important therapeutic goal. To assist in the development of more potent IDO inhibitors, the current review presents the proposed catalytic mechanisms of IDO and comprehensively reviews reported IDO inhibitors. Finally, the successful preclinical application of IDO inhibition in a new anticancer modality is described.